A rocket motor being developed by researchers at Surrey University looks set to help slash the cost of moving small satellites from one orbit to another.

The 350N "hybrid" motor has already been successfully tested by the university's Centre for Satellite Engineering Research at a British Aerospace testing facility in Buckingham.

Jerry Sellers, project leader at the centre, says that it is possible for a small satellite to get a cheap "piggy-back" ride into space aboard the Ariane rocket, for example, as part of a bigger space mission.

The orbit of the small satellite, however, is dictated by the requirements of the major satellite being put into orbit. Moving it to another orbit, if this is necessary to complete its mission, is potentially very expensive.

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This is because conventional satellites rely on either all-liquid or all-solid propulsion systems to manoeuvre in space.

But these are much too expensive for small, low-cost satellites of the type the centre specialises in developing.

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A hybrid rocket motor combines the two propulsion systems and uses both solid fuel and a liquid oxidiser to make the fuel burn. It is also safer and more environmentally friendly. "It is virtually impossible for one to explode and so it is ideal for safe experimentation and development within a university," says Captain Sellers.

The motor can easily be turned off by stopping the flow of oxidiser and then restarted later. It can also be throttled. "A hybrid rocket combines the storability of a solid system with the restart and throttle ability of a liquid system," he says.

The centre is keen to apply hybrid motor technology to mini-satellites weighing between 200kg and 300kg, and about a metre in diameter and a metre high. As well as helping to cut the cost of moving satellites from one orbit to another, Captain Sellers says that the new motor promises to help restore satellites to their correct orbit from which they have strayed because of drag or other forces.